The present invention relates generally to magnetic field sensors.
A typical vehicle includes numerous sensors that are used to monitor many physical parameters necessary to ensure the proper operation of the vehicle and its subsystems. For example, crank and cam sensors are used to sense the angular motion of the engine crank and cam shafts to ensure that the engine is running properly, e.g., that the ignition system is properly timed. Typically, these devices operate by distinguishing between high and low slots formed in a rotating targeting wheel opposite the sensor. For maximum sensitivity, two magnetoresistive (MR) die must be centered exactly (xc2x113 xcexcm) on a permanent magnet so the signals from the MR die are symmetrical and intersect precisely in the center of the slots formed in the target wheel.
It happens that the traditional method of packaging such an MR device includes placing two MR die on a very precise, and relatively expensive, leadframe and then locating the permanent magnet relative to the leadframe. In this method, the placement of the MR die and the magnet is performed blind relative to each other. More specifically, a theoretical magnet center is calculated from the leadframe dimensions and the MR die are placed on the leadframe based on this calculated center. Unfortunately, basing the placement of the MR die on this theoretical center results in a reduction in precision.
The present invention has recognized these prior art drawbacks, and has provided the below-disclosed solutions to one or more of the prior art deficiencies.
A magnetoresistive sensor assembly includes a housing. At least one permanent magnet is disposed within the housing, and at least two magnetoresistive dies are placed proximal to the magnet. Furthermore, at least three leads extend from the housing. The leads are electrically connected to the magnetoresistive dies. Additionally, the leads are part of a leadframe that forms plural slots. As intended by the present invention, the slots facilitate placement of the magnetoresistive dies based on the placement of the magnet on the leadframe.
In a preferred embodiment, the leadframe includes at least four identical sections. Each section of the leadframe forms plural long slots and plural short slots. The magnet is attached to the leadframe such that at least a portion of the magnet is visible through the frame in order to facilitate placement of the magnetoresistive dies with respect to the magnet. Preferably, the magnetoresistive dies are connected to the leads using a wire bonding process, and the leadframe and the leads are made from copper. In a preferred embodiment, the magnet, and the magnetoresistive dies are attached to the leadframe, the housing is installed around the magnet and the magnetoresistive dies, and the sensor assembly is separated from the leadframe.
In another aspect of the present invention, a method for manufacturing a sensor includes providing a leadframe that forms plural slots. At least one magnet is attached to the leadframe such that at least a portion of the magnet is visible through the leadframe. Moreover, at least two magnetoresistive dies are attached to the leadframe based on the visible portion of the magnet.
In yet another aspect of the present invention, a leadframe used in a process to manufacture a sensor assembly includes at least one section that forms plural long slots and forming plural short slots.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: